Abstract: The test facility for negative ion source is mainly used to test the performance of negative ion source in the neutral beam injection system for future magnetic confinement fusion device. The performance characteristics and test methods of the negative ion beam source were analyzed. Based on engineering and physical design requirements, this study has completed the structural design of the vacuum vessel for the negative ion source test facility of a high-power negative ion source based neutral beam injection system (NNBI) with a box-shaped shell as the structure mode for the first time in China, and the important components were integrated. The static mechanical characteristics of the vacuum vessel were numerically analyzed by using the software ANSYS Workbench, the distributions of stress and deformation were obtained, and the stress was evaluated by the method of stress linearization classification. Also, the structure of the back head with the largest deformation in the beam line vessel was optimized by using the response surface method. The final results showed that the structural strength and deformation of the vacuum vessel met the requirements of engineering design, and the deformation amplitude of the optimized head decreased significantly. This study lays a foundation for the integrated design, optimization and construction of the negative ion source test facility, which has engineering application value.